First, we researched a lot on air resistance because that was the variable that we knew the least amount of information on. One thing we found out about air resistance is that an object will experience air resistance when it is in the Earth’s atmosphere. The variables and units on how to calculate air resistance are: density of air (p) which is around 1.2kg/m3, cross sectional area of an object (A) for a sphere it would be r2, drag coefficient (Cd) which needs to be calculated separately depending on each object, and magnitude of velocity squared (v) (Allain).
The faster the object, the more air resistance it will experience. The direction of air resistance is always opposite to the direction of velocity. Terminal velocity is when an object’s initial speed is the speed of gravity but as it speeds up air resistance does as well eventually equalling back to the speed of gravity (Allain) . Another topic we did extensive research on is drag. Drag is basically the opposite force of weight.
Drag, also known as resistance, depends on the square of velocity. When an object is falling it experiences two forces, gravitational (weight) and drag, when drag and gravity are equal, acceleration is 0 and terminal velocity is constant. NASA’s equation for calculating drag is: D = Cd * p * v2* a / 2. The “p” in the equation is not actually a p but instead a Greek symbol called “rho”, which equals gas density (Hall, Falling Objects/Drag). Using the drag coefficient model, scientists are able to put drag to the test in terms of shape, inclination, and conditions involving flow. NASA was generous enough to give the drag coefficients of commonly used objects in these type of experiments. Of the examples, we will be using a prism and a sphere (Hall, Falling Objects/Drag). A prism has a drag coefficient of 1.
14 and a sphere has a drag coefficient of .07 to .5.
It is said that scientists at a NASA research center measured these coefficients while placed in a wind tunnel and measuring the amount of drag(Hall, Falling Objects/Drag) . The greater the angle, the greater the drag and when the angle is small, drag is basically constant. The immensity of the drag of an object is dependent on the shape and its movement through the air (Hall, Factors that Affect Drag). When an object is falling, it is said that the air molecules will stick to the surface that is pointing down on the object.
The air molecules are a factor that affect drag. These air molecules all combine and act as if they are apart of the object, creating a new shape. When the layer of air molecules is separated from the object, the object stalls and both drag and lift become unsteady (Hall, Factors that Affect Drag). Another factor that affects drag is the velocity of the air. Drag depends on the velocity of the object as well as the mass of the air flowing past the object. Another variable that drag takes account of is the roughness of a surface. “With the drag equation, you can predict how much drag force is generated by a given body moving at a given speed through a given fluid,” (Hall, Factors that Affect Drag). Acceleration is the time rate-of-change of velocity, in other words, it is defined as the ratio of the change in its velocity of the time elapsed in the process.
The equation for calculating average acceleration is a = Change in VelocityTime Elapsed with the units for acceleration being m/s2. When there is more than one velocity, you subtract the final velocity from the initial velocity. The same goes for time (Hecht, Chapter 3: Kinematics: Acceleration). Motion occurs in 2 basic forms: translational and rotational. An object is translational if a line drawn between any two of its internal points remains parallel to itself. An object is rotational when the line does not remain parallel to itself(Hecht, Chapter 8: Rotational Motion).
